Surface-based prostate registration with biomechanical regularization

Adding MR-derived information to standard transrectal ultrasound (US) images for guiding prostate biopsy is of substantial clinical interest. A tumor visible on MR images can be projected on US by using MR-US registration. A common approach is to use surface-based registration. We hypothesize that using biomechanical modeling will better control deformation inside the prostate than a regular surface-based registration method. We developed a novel method using a surface-based registration and extended it with finite element (FE) simulation to predict internal deformation of the prostate. For each patient, a tetrahedral mesh was constructed from the manual prostate segmentation. Next, the internal prostate deformation was simulated using the derived radial surface displacement as boundary condition. The deformation field within the gland was calculated using the predicted FE node displacements and thin-plate spline interpolation. We tested our method on MR guided MR biopsy imaging data as landmarks can easily be identified on MR images. For evaluation of the registration accuracy we used 45 landmarks located in all regions of the prostate. Our results show that the median target registration error of a surface-based registration with biomechanical regularization is 1.88 mm, which is significantly different from 2.61 mm without biomechanical regularization. We can conclude that biomechanical FE modeling has the potential to improve the accuracy of multimodal prostate registrationwhen comparing it to regular surface-based registration.